1. Field of the Invention
The present invention relates in general to torsion damping devices comprising at least two coaxial parts mounted to rotate relative to one another within defined limits of angular displacement against elastic means adapted to act circumferentially between them over at least part of such angular displacement.
2. Description of the Related Art
Such a device has been described in French Patent Application No. 2568640 from which U.S. Pat. No. 4,655,337 claims priority.
In this document meshing means with clearance are provided between the hub flange 12 and the hub 10 as well as elastic means with low strength, whilst stiffer elastic units 56A, 56B are interposed between the flange 12 and the auxiliary flanges 20. The elastic units 56A, 56B each consist of two coaxial spring 56'A, 56"A and 56'B, 56"B (FIG. 1).
For certain applications it is required that the slope of the curve representing the intervention of the relatively stiff elastic units should be gentle, whilst transmitting a large torque at the end of the action.
In relation to the above mentioned requirement (FIG. 14) it can be seen that if it is desired to decrease the slope of curve II whilst transmitting the same torque at the end of the action, the angular movement between the parts to be damped must be further increased.
Taking into account the mechanical resistance of the parts, which depends particularly on the openings for housing the springs, it can be established that an impossible situation will be reached. That is all the more so because in this patent the angular movement is very large.
An attempt can be made to modify the damping device radically, but besides this not always being possible because of the space limitations which must be taken into account, this is done to the detriment of standardization of fabrication.